Angular position detection device having linear output characteristics

ABSTRACT

An angular position detection device has a rotor that comprises two magnets and a primary yoke, and a stator that comprises a pair of auxiliary yokes and a magnetism detection element. The rotor is fixed to a rotary shaft of an object to be detected. The primary yoke forms a magnetic circuit in a ring, and the magnets are configured so that the intensity distribution of the magnetic field is asymmetric with respect to the center of rotation of the rotor. The magnetism detection element is placed in a gap between the auxiliary yokes. This stator is disposed in the inside of the rotor so that an air gap between the rotor and the stator varies gradually in the circumferential direction. Thus, the magnetism detection element is enabled to produce a linear output over a range wider than 180°.

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application relates to and incorporates herein byreference Japanese Patent Application NO. 2000-102385 filed Apr. 4,2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an angular position detectiondevice which detects an angular position of an object by use of amagnetism detection element.

[0004] 2. Related Art

[0005] As a prior art, an angular position detector is proposed inJP-A-61-75213. This angular position detector is constructed so that acylindrical magnet is magnetized in the radial direction, and amagnetism detection element is disposed in the middle of the magnet, andthe magnet (or the magnetism detection element) rotates with rotation ofan object to be detected. In this construction, if the magnet rotates,the amount of magnetic flux passing through the magnetism detectionelement varies and an output signal from the magnetism detection elementvaries with the amount of the magnetic flux. Thus the angular positionof the object to be detected is detected by means of the output signal.

[0006] In the case of detecting the angular position of the object to bedetected by means of the output signal from the magnetism detectionelement in this way, in order to expand a range of detection of theangular position, characteristics of the output variation in themagnetism detection element against the angular position need be madelinear over as wide a range as possible.

[0007] However, in the above prior art, since the parallel magneticfield is rotated about the magnetism detection element, the magnetismdetection directional component of the magnetic flux passing through themagnetism detection element decreases in trigonometric function as theangular position advances. As a result, the characteristics of theoutput variation in the magnetism detection element against the angularposition deviates from the straight line and curves in trigonometricfunction. Therefore the prior art has a problem that it provides only apseudo-linear output over a narrow range of the angular position.

[0008] In contrast to this, in U.S. Pat. No. 5,861,745, as shown inFIGS. 9A to 9D, an angular position sensor which is constructed so thatsemicircular auxiliary stators 110 are installed on both sides of amagnetism detection element 100 so that the air gap between acylindrical magnet 120 and the auxiliary stators 110 is uniform. In thisangular position sensor, the direction of the magnetic flux passingthrough the magnetism detection element is always perpendicular to thedirection of magnetism detection by the auxiliary stators, and theamount of the magnetic flux passing between the auxiliary stators 110changes with rotation. Thus it provides a linear output over a widerrange of the angular position.

[0009] However, in the above angular position sensor, since a magneticcircuit is formed in point symmetry, the positional relation is the sameexcept that the poles of the magnet 120 are reversed when it is rotated180°. Accordingly, as shown in FIGS. 9A to 9D, the maximum or minimumpoints (peak points) appear at every 180°. That is, a range in which theoutput is linear is a maximum of 180° (between −90° and 90°), and it isimpossible to provide a linear output over a wider range than this.Practically, since characteristics in the vicinity of the peak points isnot perfectly linear, the actual linear range is limited to 160°.

SUMMARY OF THE INVENTION

[0010] The present invention overcomes the above drawbacks, and has anobject to provide an angular position detection device which is capableof establishing linear characteristics of an output of a magnetismdetection element over a range wider than 180°, thereby improvingcharacteristics of detection of an angular position.

[0011] The angular position detection device according to the presentinvention comprises one or two magnets for generating a magnetic fieldand one or more magnetism detection elements disposed in the magneticfield for detecting magnetism. The magnets are installed in a rotor andthe magnetism detection elements are installed in a stator, or viceversa. The stator is disposed in the inside of the rotor, which is fixedto a rotary shaft of an object to be detected. The stator or rotor inwhich the magnets are installed has a primary yoke that forms a magneticcircuit of the magnets, and is configured so that the intensitydistribution of the magnetic field is asymmetric with respect to thecenter of rotation of the rotor. On the other hand, the stator or rotorin which the magnetic detection elements are installed has a pair ofauxiliary yokes, and the magnetic detection elements are disposed in thegap provided between the pair. The stator and the rotor are configuredso that the air gap between them varies gradually in the circumferentialdirection.

[0012] According to this construction, since the point symmetry in themagnetic circuit does not hold, the angular interval between the peakpoints in output characteristics of a magnetism detection element islarger than 180° and thus a linear range wider than ±90° can beprovided. As a result, characteristics of detection of the angularposition can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention, together with additional objects, features andadvantages thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings in which:

[0014]FIG. 1 is a plan view showing a construction of a main part of anangular position detection device according to a first embodiment of thepresent invention;

[0015]FIGS. 2A to 2D are charts showing a relation between a rotationaloperation and an output in the angular position detection deviceaccording to the first embodiment;

[0016]FIG. 3 is a plan view showing a construction of a main part of anangular position detection device according to a second embodiment ofthe present invention;

[0017]FIG. 4 is a plan view showing a construction of a main part of anangular position detection device according to a third embodiment of thepresent invention;

[0018]FIG. 5 is a plan view showing a construction of a stator accordingto a fourth embodiment of the present invention;

[0019]FIG. 6 is a plan view showing a construction of a main part of anangular position detection device according to a fifth embodiment of thepresent invention;

[0020]FIG. 7 is a plan view showing a construction of a main part of anangular position detection device according to a sixth embodiment of thepresent invention;

[0021]FIG. 8 is a plan view showing a construction of a main part of anangular position detection device according to a seventh embodiment ofthe present invention;

[0022]FIGS. 9A to 9D are chars showing a relation between a rotationaloperation and an output of an angular position detection deviceaccording to a prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] The present invention will be described with reference toembodiments and modifications in which the same or similar parts aredesignated by the same reference characters.

First Embodiment

[0024]FIG. 1 is a plan view showing a construction of a main part of anangular position detection device according to a first embodiment of thepresent invention. The angular position detection device is used as, forexample, a throttle position sensor in a motor vehicle. As shown in FIG.1, the device has a rotor that comprises two magnets 1 (a first magnet 1a, a second magnet 1 b) and a primary yoke 2, and a stator thatcomprises a pair of auxiliary yokes 3 and a magnetism detection element4. The rotor is fixed to a rotary shaft of a throttle valve (not shown).

[0025] Each of the magnets 1 is installed in arcuate arrangement, andmagnetized so that one end in the circumferential direction is the northpole and the other end is the south pole.

[0026] The primary yoke 2 is made of a magnetic material such aspermalloy or iron, and it closes the distance between the two magnets 1in a ring to form a magnetic circuit. The magnets 1 are placed so thatthe angle (central angle) α, which is formed between the radius a thatconnects the first magnet 1 a and the center Or of the rotor and theradius b that connects the second magnet 1 b and the center Or of therotor, is less than 180° (for example, 90°). The same poles of the twomagnets face each other in the circumferential direction as shown inFIG. 1. In this case, magnetic flux produced by the two magnets areconducted along the primary yoke and repel each other. As a result, auniform magnetic field in which the magnetic flux flows radially isgenerated in the internal space of the primary yoke. Furthermore, theintensity distribution of the magnetic field is asymmetric with respectto the center of rotation of the rotor.

[0027] The pair of auxiliary yokes 3, which induces magnetic flux in themagnetism detection element 4, is made of a magnetic material such aspermalloy or iron, similarly to the primary yoke 2, and installed innearly semicircular arrangement respectively. The pair of auxiliaryyokes 3 is disposed so that their flat surfaces face each other inparallel and a gap 5 is provided between them. It is constructed so thatthe general shape of the pair of auxiliary yokes 3 is circular.

[0028] The magnetism detection element 4 is, for example, a well-knownHall element, which outputs a voltage signal corresponding to theintensity of the magnetic field. The magnetism detection element 4 isplaced in the gap 5 provided between the auxiliary yokes 3, and disposedso that the direction of magnetism detection by the element isperpendicular (toward the horizontal direction in FIG. 1) to thedirection of the gap (the vertical direction in FIG. 1).

[0029] The stator, which comprises the pair of auxiliary yokes 3 and themagnetism detection element 4, is disposed within the rotor, and an airgap G is provided between the rotor and the stator. The air gap G isprovided to vary gradually along the circumferential direction.Specifically, as shown in FIG. 1, the stator is disposed so that thedirection of the gap in the stator is aligned with the centerline A-A ofthe rotor, and the center Os of the stator is offset a predetermineddistance L from the center Or of the rotor. Hereafter, in the followingexplanation of operation, the position of the rotor shown in FIG. 1 isassumed to be ‘0°-position’, and the direction of rotation of the rotoris clockwise in FIG. 1.

[0030] Next the operation and the effect of the angular positiondetection device constructed as described above is described withreference to FIGS. 2A to 2D.

[0031] First, when the rotor is in ‘0°-position’, the pair of auxiliaryyokes 3 is in the line symmetrical position with respect to thecenterline A-A of the rotor shown in FIG. 1. In this case, in the insideof the rotor, the direction of the magnetic flux passing through theauxiliary yokes 3 is perpendicular to the direction of magnetismdetection by the magnetism detection element 4 as shown in FIG. 2A.Therefore detected magnetic force is zero as shown in FIG. 2D.

[0032] Thereafter, when the rotor rotates with rotation of the throttlevalve, the direction of the magnetic flux in the inside of the rotorvaries, and the air gap G between the auxiliary yokes 3 and the magnets1 also varies. Here, in case of a conventional device (FIGS. 9A to 9D)in which the center of rotation of the rotor coincides with the centerof the stator, detected magnetic force is the largest when the rotorrotates up to ‘90°-position’ where the direction of the magnetic flux inthe inside of the rotor is parallel with the direction of magnetismdetection by the magnetism detection element 4. If the rotor furtherrotates, the detected magnetic force decreases. When the rotor rotatesup to ‘180°-position’, the detected magnetic force becomes zero again.

[0033] In contrast to this, in the angular position detection deviceaccording to the present embodiment, the center of the stator is offsetfrom the center of rotation of the rotor. Therefore, the detectedmagnetic force is not the largest when the rotor rotates up to‘90°-position’ as shown in FIG. 2B. That is, the direction of themagnetic flux against the magnetism detection element 4 in the inside ofthe rotor changes with rotation of the rotor similarly to theconventional device. However, the air gap G between the magnets 1 andthe auxiliary yokes 3 gradually becomes smaller while the rotor rotatesfrom ‘90°-position’ to ‘180°-position’, because the center of rotationof the rotor is offset from the center of the stator. When the air gap Gbecomes small, the amount of the magnetic flux passing through theinside of the auxiliary yokes 3 increases. Therefore the detectedmagnetic force continues to increase while the rotor rotates beyond‘90°-position’ as shown in FIG. 2D.

[0034] When the rotor further rotates and the direction of the magneticflux in the inside of the rotor becomes nearly perpendicular to thedirection of magnetism detection by the magnetism detection element 4,as shown in FIG. 2C, the detected magnetic force reaches its peak whenthe rotor is in some angular position (for example, ‘135°-position’) asshown in FIG. 2D. Thereafter, if the rotor further rotates, the detectedmagnetic force decreases in a higher rate, and it becomes zero when therotor rotates up to ‘180°-position’.

[0035] As a result, linear output can be provided over a range widerthan that of ‘0°-position’ ±90°.

[0036] The first magnet 1 a and the second magnet 1 b are disposed insuch positions that the central angle formed between them with respectto the center Or of rotation of the rotor is α, which is assumed to be90° in the above embodiment. The range of linear output is further widerif α is set to a smaller value, and narrower if α is set to a largervalue. Accordingly, α a may be arbitrarily set according toapplications. However, if α is set to 180°, the detected magnetic forcereaches its peak every 180°, and hence the effect of the improvement ofexpanding the range of linear output cannot be provided. Therefore αmust be set to a value less than 180°.

Second Embodiment

[0037]FIG. 3 is a plan view showing a construction of a main part of anangular position detection device according to a second embodiment ofthe present invention. In the present embodiment, the primary yoke 2 ofthe rotor is cut along the centerline A-A and divided into a right yoke2 a and a left yoke 2 b, and gaps 6 are provided between them. In thiscase, since magnetic reluctance between the right and left yokes 2 a, 2b increases due to the gap 6, the adverse effect of demagnetization dueto repellence of the magnetic flux from the magnets 1 a, 1 b in theinside of the primary yoke 2 is alleviated.

[0038] The gap 6 may be provided only in the upper portion of theprimary yoke 2 shown in FIG. 3, because the adverse effect of thedemagnetization due to the repellence of the magnetic flux issignificant when the distance between the magnets 1 a, 1 b is short.

Third Embodiment

[0039]FIG. 4 is a plan view showing a construction of a main part of anangular position detection device. In the present embodiment, it themagnets 1 are not arcuate but rectangular (rectangular parallelopiped).In this case, since magnets 1 are manufactured by the simplest formingprocess and the simplest magnetization process (parallel magnetization),magnets 1 of even and high quality can be manufactured at low cost.

Fourth Embodiment

[0040]FIG. 5 is a plan view showing a construction of the statoraccording to a fourth embodiment of the present invention. In thepresent embodiment, more than one magnetism detection element 4 isemployed.

[0041] Since the direction and intensity of the magnetic field in thegap 5 provided between the pair of auxiliary yokes 3 are uniform, aplurality of magnetism detection elements 4 can be disposed in the gap 5and almost the same angular position signal can be obtained from eachelement 4. Thus a sensor which has two or more outputs can beconstructed. Furthermore, even if one magnetism detection element 4fails, another magnetism detection element 4 can be used, and hencereliability of the device is improved. Moreover, precision of detectioncan be improved by comparing outputs from the magnetism detectionelements 4.

Fifth Embodiment

[0042]FIG. 6 is a plan view showing a construction of a main part of anangular position detection device according to a fifth embodiment of thepresent invention. In the present embodiment, only one magnet 1 is used,and it is disposed on inner perimeter side of the primary yoke 2 so thatone pole face toward the center of rotation of the rotor.

[0043] In this case, by using the one magnet, magnetic flux that flowsradially in the primary yoke is produced similarly to the case of usinga plurality of magnets, so that linear output can be provided over arange wider than 180° similarly to the first embodiment.

Sixth Embodiment

[0044]FIG. 7 is a plan view showing a construction of a main part of anangular position detection device according to a sixth embodiment of thepresent invention. In the present embodiment, the angular positiondetection device is constructed so that the center Os of the stator isaligned with the center Or of rotation of the rotor and the air gap Gbetween them varies in the circumferential direction.

[0045] In order that the air gap G between the magnets 1 and theauxiliary yokes 3 varies with rotation of the rotor, as shown in FIG. 7,the shape of the auxiliary yokes 3 may be changed instead of offsettingthe center Os of the stator from the center Or of rotation of the rotor.Alternatively, the shape of the rotor may be changed to a shape (forexample, an elliptic cylinder) other than the ring (the shape shown inthe first embodiment).

Seventh Embodiment

[0046]FIG. 8 is a plan view showing a construction of a main part of anangular position detection device according to a seventh embodiment ofthe present invention. In the present embodiment, a portion of theprimary yoke 2 is removed between the north pole sides of the twomagnets 1 a, 1 b in contrast to the construction of the rotor explainedin the first embodiment.

[0047] In this case, similarly to the first embodiment, linear outputcan be provided over a range wider than 180°.

Modifications

[0048] In the above embodiments, the magnets 1 may be disposed with itsmagnetic poles reversed.

[0049] Furthermore, a stator may comprise the magnets 1 and the primaryyoke 2 and a rotor may comprise the pair of auxiliary yokes 3 and themagnetism detection element 4, in contrast to the above embodiments inwhich the rotor comprises the magnets 1 and the primary yoke 2 and thestator comprises the pair of auxiliary yokes 3 and the magnetismdetection element 4.

What is claimed is:
 1. An angular position detection device comprising amagnet device for generating a magnetic field and a magnetism detectiondevice disposed in the magnetic field for detecting magnetism, one ofsaid magnet device and said magnetism detection device being installedin a stator and the other being installed in a rotor, so that an angularposition of said rotor is detected based on an output from saidmagnetism detection device, wherein said stator or said rotor in whichsaid magnet device is installed is configured so that an intensitydistribution of the magnetic field is asymmetric with respect to acenter of rotation of said rotor, and wherein said stator and said rotorare configured so that an air gap between them varies gradually in acircumferential direction.
 2. An angular position detection device as inclaim 1 , wherein said stator or said rotor in which said magnetismdetection device is installed includes a pair of auxiliary yokes thatinduces magnetic flux in said magnetism detection device, wherein a gapis provided between the pair of auxiliary yokes, and wherein saidmagnetism detection device is disposed in the gap.
 3. An angularposition detection device as in claim 2 , wherein said pair of auxiliaryyokes is installed so that a general outer shape of the pair is nearlycircular, and a center of the pair is offset from the center of rotationof said rotor.
 4. An angular position detection device as in claim 2 ,wherein said magnetism detection device includes a plurality ofmagnetism detection elements disposed in the gap provided between saidpair of auxiliary yokes.
 5. An angular position detection device as inclaims 1, wherein said rotor or stator in which said magnet device isinstalled includes a primary yoke that forms a magnetic circuit of saidmagnet device, and wherein said primary yoke is formed in an arcuateshape which has a constant distance from the center of rotation of saidrotor.
 6. An angular position detection device as in claim 5 , whereinsaid rotor or stator which includes said primary yoke has two magnets assaid magnet device, and wherein said magnets are disposed so that anangle between them with respect to the center of rotation of said rotoris less than 180° and the same poles face each other in thecircumferential direction.
 7. An angular position detection device as inclaim 6 , wherein a gap is provided in said primary yoke so that themagnetic circuit is separated between the magnets.
 8. An angularposition detection device as in claim 5 , wherein said rotor or statorwhich includes said primary yoke has only one magnet as said magnetdevice, and wherein said magnet is placed so that one pole of saidmagnet face toward the center of rotation of said rotor.
 9. An angularposition detection device as in claim 1 , wherein said magnet device hasa circular yoke and a pair of magnets arranged in said yoke within arange of 180° with respect to a center of said yoke.
 10. An angularposition detection device as in claim 1 , wherein said rotor and saidstator are formed in generally circular shape having differentdiameters, and wherein said centers of said rotor and said stator areoffset from each other.
 11. An angular position detection device as inclaim 1 , wherein said rotor is fixed to a rotary shaft of a throttlevalve.